Among the air conditioners arranged in office buildings and general residential buildings, and the like, split-type systems having an indoor unit and an outdoor unit are widely used. In this kind of an air conditioner, a refrigerant circuit is often times formed by a compressor and an outdoor heat exchanger included in the outdoor unit, an expansion valve and an indoor heat exchanger included in the indoor unit, and a refrigerant communication pipe for connecting these equipments. Heat exchange can be done at the outdoor heat exchanger and the indoor heat exchanger, through refrigerant circulating through this kind of a refrigerant circuit. In addition, normally in this kind of an outdoor unit, an outdoor fan is arranged for encouraging heat exchange in the outdoor heat exchanger.
In the case that cooling operation is performed under a condition that the temperature of outside air is comparatively low during a time such as between seasons, if the outdoor fan rotates excessively, there might be a problem that there will not be a sufficient differential pressure between the pressure of the refrigerant on the intake side and the pressure of the refrigerant on the discharging side of the compressor. In this kind of a situation, problems such as the reverse rotation of the compressor, circulating amount dropping can occur, and this lowers the reliability of the compressor.
Consequently, as described in JP-A Publication No. 2002-39589, conventionally, if the differential pressure between the high and low pressure of a compressor cannot be kept sufficiently, a control for lowering the rotational speed of the outdoor fan is performed. More specifically, in Patent Document 1, a maximum value for the rotational speed of the outdoor fan is set according to the state of the differential pressure between the high and low pressure of the compressor.